X-ray photography is used in a variety of medical fields.
A mammography machine is a kind of X-ray photography machine which is used to detect breast cancer, lesions, microcalcification, etc. A representative conventional mammography machine was proposed in Korean Patent Laid-open Publication No. 10-2009-0112992 (entitled: Mammography machine having large-area digital sensor).
To examine the breast of a patient, the breast that is to be examined must be pressed. Thus, mammography machines include a pressing member which presses the breast, and a transfer apparatus which moves the pressing member.
Typically, when the pressing member presses the breast, the patient feels pain and discomfort. Particularly, if an unexpected event such as power failure occurs, the pressing member may be stopped while the breast is being pressed by the pressing member. In this case, the patient will almost certainly experience a sense of fear or embarrassment. Therefore, when an unexpected event occurs, the pressing member must be able to release the breast.
FIG. 1 is a sectional view illustrating a conventional transfer apparatus (at present, unpublished) for mammography machine which was proposed by the applicant of the present invention. This transfer apparatus is configured such that, upon power interruption, a breast pressing operation is automatically stopped so as to release the breast of a patient.
The transfer apparatus 170 of FIG. 1 includes a drive motor 171, a drive pulley 172a, a driven pulley 172b, a drive belt 173, a first drive shaft 174, a first pulley 175a, a second pulley 175b, a switch belt 176, a second drive shaft 177, a coupling member 178 and a clutch 179.
The first drive shaft 174 is interlocked with the drive pulley 172a, the driven pulley 172b and the drive belt 173.
The second drive shaft 177 is interlocked with the first pulley 175a, the second pulley 175b and the switch belt 176.
The coupling member 178 is coupled at a first side thereof to the switch belt 176. A second side of the coupling member 178 is coupled to a pressing member.
The clutch 179 has an effect of making the second drive shaft 177 dependent on the rotation of the first drive shaft 174. For this, the clutch 179 includes a first flange 179a which is interlocked with the first drive shaft 174, and a second flange 179b which is interlocked with the second drive shaft 177.
The first flange 179a generates magnetic force when power is supplied thereto. Thus, upon power being supplied, the second flange 179b is attached to the first flange 179a by the magnetic force of the first flange 179a. In this case, the second flange 179b can be rotated in conjunction with the rotation of the first flange 179a. 
When the power is interrupted, the magnetic force of the first flange 179a is removed. Then, the second flange 179b is separated from the first flange 179a. As a result, the pressing member that has been pressing the breast of the patient automatically releases the breast.
Meanwhile, as shown in FIG. 2, the tension T1 of the drive belt 173 and the tension T2 of the switch belt 176 respectively act as rotation momentum R1 to the first drive shaft 174 and as rotation momentum R2 to the second drive shaft 177. Thereby, the first drive shaft 174 rotates around a first bearing B1 within an allowance range (based on a tolerance or the like). The second drive shaft 177 rotates around a second bearing B2 within an allowance range (based on a tolerance or the like). Therefore, the rotating axes of the first drive shaft 174 and the second drive shaft 177 may be misaligned with each other rather than being parallel to each other. As a result, the drive belt 173 and the switch belt 176 may be biased to one side (refer to the arrows a and b of FIG. 2). If the drive belt 173 or the switch belt 176 that has been biased to one side makes contact with a flange portion H1 or H2 of the pulley 172b or 175a, noise is generated. Of course, the durability of the drive belt 173, the switch belt 176 and other elements may also be reduced.